A porous vitrified grinding stone is known that has abrasive grains such as CBN abrasive grains, diamond abrasive grains, or an ordinary abrasive grains bound therein using a vitreous inorganic binder. Such a vitrified grinding stone is formed as, for example, an arc-shaped grinding stone piece and a plurality of such pieces are used as a vitrified grinding wheel that is formed by fixing the pieces using an adhesive on the outer circumferential surface of a disc-shaped core such as a base metal piece made of a metal or a ceramic core made of an inorganic material such as a vitrified structure. Such a vitrified grinding wheel provides a high grinding ratio and high grinding efficiency, and is advantageously used when a work to be ground such as a metal part or a hardened-steel product is ground at a high speed. For example, types of vitrified super-abrasive-grain grinding stone described in Patent Documents 1 and 2 correspond to the above vitrified grinding stone.